The semiconductors memory has been playing core role in the development of the semiconductor technology, holding an irreplaceable position in various information technology (IT) fields. Currently, the mainstream semiconductor memory includes a volatile dynamic random access memory (DRAM) and static random access memory (SRAM), and a nonvolatile flash memory (Flash). However, as the technology advances, that is, as the critical dimension continuously reduces and the integration degree constantly increases, the scaling of the DRAM, SRAM and Flash is reaching the limitation, especially in the circumstance of entering a nanometer technology node. In particular, the performance of the parameters of the nonvolatile memory fluctuates randomly and significantly, resulting in more and more severed reliability problems. Under such circumstances, through researches of a variety of technology solutions such as new materials, new structures and new functions, new technologies for the nonvolatile memory, including a charge trapping memory (CTM), a ferroelectric random access memory (FeRAM), a magnetic random access memory (MRAM), a phase change random access memory (PRAM) and a resistive random access memory (RRAM), have been suggested. Among them, the resistive random access memory has gained widespread attention due to its excellent performance in various aspects, and has become a research focus for the next generation mainstream memories.
The resistive random access memory stores information based on the resistive characteristic of the storage medium, which is a property for certain dielectric materials that the resistance changes reversibly between a high and a low resistance state under an externally-applied electrical field. Further, the resistive random access memory is classified into an inorganic resistive random access memory and an organic resistive random access memory based on different resistive material used therein. In the prior art, the inorganic resistive random access memory, which is fabricated based on transition metal oxide (TMO), is dominant due to the advantages such as simple processes and low costs. A structure of the TMO-RRAM is shown in FIG. 1. Two electrodes are applied with a voltage V. In an initial state, the resistive random access memory is in a high resistance state. When the voltage V is increased to a certain value, the resistive random access memory is changed from the high resistance state to a low resistance state. Such a process is referred to as a forming process, and the voltage V corresponding thereto is defined as Vform. The low resistance state may be maintained for a long period even if a voltage supply is cut off. And after the voltage is further increased to a certain value, the resistive random access memory returns to the high resistance state. Such a process is referred to as a resetting process, and the voltage V corresponding thereto is defined as Vreset. Similarly, the high resistance state may be maintained for a long period even if a voltage supply is cut off. And after the voltage is further increased to a certain value, the resistive random access memory returns to the low resistance state. Such a process is referred to as a setting process, and the voltage V corresponding thereto is defined as Vset.
Currently, a mainstream opinion is that the metal oxide based resistive random access memory has the resistive characteristic based on a conductive filament mechanism. That is, the high and the low resistance states correspond to a formation process and a rupture process of the conductive filament, respectively. When V=Vset, the electric field causes metal ions or oxygen vacancies to move directionally so that a conductive channel is formed in a local region to connect a top electrode with a bottom electrode, which corresponds to the low resistance state. On the other hand, when the voltage becomes Vreset, the channel is ruptured due to a combined effect of the electric filed and the heat, resulting in that the resistive random access memory becomes the high resistance state.
Because of the fact that the formation location, the length and the size of the conductive channel in the resistive random access memory are random, parameters exhibited by the resistive random access memories may fluctuate depending on various memories or various switching processes, and thus a uniformity problem of the memories is caused. During the repeated reading operations, the metal ions and the oxygen vacancies may diffuse into surroundings so that the performance of the resistive random access memory is deteriorated, which causes a reliability problem. The present invention is to provide a solution directing to the above two aspects.